Problems

Pollutants are a serious threat to the ecosystems of the St. Laurence, and affect all levels of the food chain. When larger animals eat contaminated smaller organisms, toxins build up in their bodies.

Birds and marine mammals living in polluted habitats can be severely affected by the toxic substances they ingest when feeding.

The cargo ships, oil tankers and cruise ships that sail the St. Lawrence emit sounds that affect large whales, as they overlap with the frequencies many whale species use to communicate and orient themselves. Noise pollution can interfere with whales' ability to detect ships, increasing the risk of a fatal collision. Ships can also mask the ultrasounds whales use to locate their food. High ship traffic can therefore degrade whale habitat. Whales can also get tangled in fishing gear.

This dolphin, which is a type of toothed whale, was designated as "not at risk" by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1991. Conversely, the beluga is listed as a species at risk of extinction. Three Canadian whale populations are at risk: Southern Resident killer whales, North Atlantic right whales and St. Lawrence Estuary belugas.

Shoreline erosion, intensified by wave action from passing ships and pleasure craft, can result in the destruction of certain habitats. Furthermore, the concentration of water flow in the shipping channel contributes to siltation in Lake Saint-Pierre, which destroys aquatic vegetation. As the area covered by aquatic plants shrinks, the yellow perch population also declines. Juveniles of this once-abundant fish species feed in aquatic vegetation beds. The loss of these habitats means they are unable to find sufficient food to grow large enough to survive their first winter.

The 11.3 metre-deep channel dredged in the centre of Lake Saint-Pierre allows ships to cross this wide stretch of water, whose average depth is just 3 m. However, the creation of the channel destroyed numerous wetlands by lowering water levels on either side.

When the wetland vegetation along the shore is thick enough, it can stabilize the soil.

Wetlands support exceptional biodiversity. If the shipping channel is dredged any deeper, portions of the lake on either side of the channel could dry up, destroying wetland habitats.